The present invention relates to photodiodes and, more particularly, to an integrated photodiode for silicon monolithic integrated circuits.
With the rapid proliferation of fiber optic communications systems and associated opto-electronic devices, photodiodes have become increasingly important. Information in the form of optical signals is difficult to process. However photodiodes can convert optical signals to electrical signals, and the resulting electrical signals can be efficiently and reliably processed by one of the very large number of compact, complex and inexpensive processing circuits now available in monolithic integrated circuits through silicon VLSI technology.
However one difficulty that has been encountered in the marriage of optical and VLSI technology is the absence of a reliable monolithically integrated silicon photodiode. Because of silicon's low absorption characteristics, photons of interest can often penetrate to depths greater than can be readily controlled by conventional planar technology. As a consequence, free carriers photonically generated deep within the substrate can disrupt nearby integrated circuit components. In addition, nearby components must be isolated from the DC bias voltage used with the photodiode.
Because integrated photodiodes have generally been incompatible with proper functioning of the other components of a VSLI integrated circuit, most optoelectronic devices employing photodiodes and silicon monolithic integrated circuits have been hybrid structures employing separately fabricated photodiodes in conjunction with separately fabricated amplifying and processing circuits. This hybrid approach increases cost and reduces reliability and performance.